(1) Field of the Invention
This invention relates to an ion sensor using an ion carrier membrane selectively permeable to an ion of interest.
(2) Description of the Prior Art
A known method of measuring a specific ion concentration in a liquid specimen uses a spectrum based on flame analysis. However, the method is disadvantageous in that it involves an apparatus of large size, cannot be applied for use at the site where the diagnosis is made and requires a long period of time to effect measurement.
An ion sensor known to be free of these disadvantages is a liquid-membrane electrode which uses a polymeric membrane that supports valinomycin, and which is provided with an internal liquid chamber. Owing to the provision of the internal liquid chamber, however, it is difficult to miniaturize the apparatus, and such problems as leakage and contamination are encountered.
To eliminate the drawbacks of the conventional ion sensor comprising the aformentioned liquid-membrane electrode, an ion sensor in which an ion-sensitive substrate is directly coated with an ion carrier membrane has been proposed. However, directly coating the ion-sensitive substrate with the ion carrier membrane uniformly to a desired thickness is not easy. For example, though a dip-coating method has been contemplated as the general means for obtaining the coating, it is difficult to adjust the viscosity of the dipping solution, the rate at which the substrate is lifted from the dipping solution, and the drying conditions. As a result, a variance tends to occur in membrane thickness. Another problem is that the process is troublesome and time consuming.